1820 in Wales

Centuries:	17th; 18th; 19th; 20th; 21st;
Decades:	1800s; 1810s; 1820s; 1830s; 1840s;
See also:	List of years in Wales; Timeline of Welsh history 1820 in The United Kingdom Scotland Elsewhere

This article is about the particular significance of the year 1820 to Wales and its people.

Incumbents

29 January – The Prince of Wales becomes King George IV on the death of King George III of the United Kingdom.
14 April - At the completion of the United Kingdom general election:
- Henry Paget, later Marquess of Anglesey, is elected as member for Anglesey.
- Wyndham Lewis is elected for Cardiff.
- Christopher Cole is re-elected for Glamorganshire.
The first "colliery school" in the South Wales coalfield is established at Hirwaun.
Thomas Price (Carnhuanawc) founds a Welsh school at Gelli Felen.
Crawshay Bailey becomes a partner at Nant-y-glo ironworks with his brother, Joseph Bailey.
The Honourable Society of Cymmrodorion is revived, having been in abeyance since 1787.
John Scandrett Harford meets Bishop Thomas Burgess and offers to donate the site of Lampeter Castle for the construction of St David's College.
Tondu Ironworks is built by Sir Robert Price.

20 January - Eliezer Williams, clergyman and genealogist, 75
29 January – King George III of the United Kingdom, Prince of Wales 1751–1760, 81
16 June – Thomas Jones of Denbigh, Methodist preacher and writer, 64
27 June – William Lort Mansel, bishop and academic, 67
23 August – Edward Randles, harpist, 57
28 August – Henry Mills, musician, 63